The present invention relates to a male portion, a drill bit and a threaded joint for percussive rock drilling.
1. Prior Art
In percussive top hammer drilling in rock, a drill string is intended to be fastened in a shank adapter in a drilling machine via one end surface of a rod element or a tube element. The other end of the rod or tube is threaded either to another rod or to another tube or to a drill bit for percussive drilling. The rod or the tube can also be fastened to the shank adapter or another detail by means of threaded sleeves. A flush channel runs through the entire drill string in order to lead flush medium to the drill bit to coil away drill cuttings.
At drilling the drill string, i.e., crowns, rods, tube, sleeves and shank adapters, is subjected to mechanical and corrosive attack. This applies especially when drilling below earth where water is used as flush medium and where the environment is humid. Attacks are especially serious at the most stressed parts, that is, in thread bottoms and other reductions, that have small cross-sectional area. The drilling tool is often subjected to bending moments in connection with the drill bit reaching a skew wall in a cavity in the rock. In combination with pulsating strain, caused by impact waves and bending stresses, fatigue or breakage arises.
2. Objects of the Invention
An object of the present invention is to considerably improve the resistance against fatigue in a drill element for percussive rock drilling.
Another object of the present invention is to considerably improve the resistance against fatigue in sections of reduced cross-sectional areas in a drill element for percussive rock drilling.
Still another object of the present invention is to considerably improve the resistance against fatigue in thread bottoms in a threaded portion in a drill element for percussive rock drilling.